a). Field of the Invention
The present invention relates an endless belt type delivery device employed in a transfer unit of a conveyor belt type which is incorporated in an image forming apparatus such as a copying machine, a printer or the like and also which carries a sheet by means of a belt and allows a toner image to be transferred onto the sheet.
b). Related Art
The above-mentioned image forming apparatus comprises, in the periphery of an image carrier, a latent image forming unit, a developing unit, a transfer unit, a cleaning unit, an electric charge removing unit and the like in the order of processes to be carried out by the image forming apparatus. In the image forming apparatus, an image can be formed in the following processes: that is, at first, an electrostatic latent image is formed on the surface of the image carrier by the latent image forming unit, the electrostatic latent image is next developed as a toner image by the developing unit, the toner image is then transferred onto a sheet by the transfer unit, after then, the residual toner on the image carrier is removed by the cleaning unit, and the electric charges of the image carrier are removed by the electric charge removing unit. In some of the image forming apparatus of this type, in more particular, in the image carrier and transfer unit of the image forming apparatus, there is employed a belt conveyor device. That is, in the case of the image carrier, the image carrier itself is formed of an endless bet and, in the case of the transfer unit, the transfer unit carries the sheet by means of an endless belt.
In such endless belt type conveyor device, an endless belt, which is wound around a drive roller and a plurality of driven rollers including a tension applying roller, is driven by the drive roller. In this driving system, however, there is a possibility that a tension applied to the belt can be biased toward the width (that is, in the axial direction of the roller) and the belt can be thereby caused to meander. If the belt meanders, in the case of the image carrier, the latent image to be formed on the belt is then biased or shifted and, in the case of the transfer unit, the toner image to be transferred onto the sheet on the belt is biased, so that a good image cannot be obtained. Especially, in a multi-color type image forming apparatus in which a multi-color image is formed by means of a toner image having a plurality of colors, such poor image can occur outstandingly.
In view of the above, there have been conventionally proposed various kinds of technologies to solve the above-mentioned problem.
Some of the technologies are as follows:
(1) In Japanese Patent Publication No. 54-24033 of Showa, there is disclosed means in which a brake roller is disposed on the outer peripheral side of a belt and a bearing for the brake roller is arranged eccentric to the brake roller, so that the leaning of the belt can be adjusted by changing the contact angle of the brake roller with respect to its opposing roller.
(2) In Japanese Utility Model Publication No. 4-87849 of Heisei, there is disclosed a technology in which one of rollers is formed as a yawing roller and the yawing roller is formed in a drum shape to thereby prevent a belt-like body to be developed (image carrier) from meandering.
(3) In Japanese Patent Publication No. 4-317936 of Heisei, there is disclosed a technology in which two edge guides each having a large diameter are provided at the two ends of a cylindrical roller and the walking of a belt can be restricted by the two edge guides.
(4) In Japanese Patent Publication No. 5-165385 of Heisei, there is disclosed a technology which detects the walking of a belt and moves a roller in the axial direction thereof based on such detection.
(5) In Japanese Patent Publication No. 4-60915 of Heisei, there is disclosed a technology in which a walking belt is made to go up onto a tapered roller and the position of the roller can be shifted due to the rotation thereof.
However, in the technology (1), since the meandering of the belt is corrected by changing the carriage direction of the belt to the lateral direction thereof in a portion of the whole peripheral length thereof, there is a fear that, when the belt meandering is corrected, an unreasonable force can be applied to the belt to thereby shorten the life of the belt. In the technology (2), since the number of the yawing roller is one, there is a limit to the adjustment of the belt meandering when the belt is long and thus the range of the employment of the present technology is limited. Also, in the technology (3), because the belt is always in contact with the edge guides, the end faces of the belt are easy to wear, the belt can be damaged due to the buckling loads given by the edge guides, and, if the belt has a seam, the seam portion of the belt can be cracked easily. That is, a satisfactory performance cannot be obtained from the viewpoint of reliability and maintainability. Also, according to the present technology, since two link mechanisms are respectively provided in the two end portions of the roller, when mounting and removing the belt, these link mechanisms provide a cause to worsen the efficiency of the belt mounting and removing operation.
Further, in the technologies (4) and (5), there is necessary a mechanism for controlling so that the structure thereof is also complicated.
The present invention provides a belt conveyor device which can solve the above-mentioned problems found in the conventional technologies.